The present invention relates to an apparatus for supporting a conveyor belt. More specifically, the apparatus of the present invention relates to a fluid plenum trough conveyor support that provides a near frictionless fluid film bearing to support a conveyor belt. The apparatus of the present invention may be used as a discrete conveyor belt support element. The discrete elements formed by the method of the present invention may also be sealingly joined to form a continuous trough conveyor path for a conveyor system. An improved particulate collection system is provided at termination points of the conveyor system for eliminating particulate emissions as the bulk materials transported by the conveyor are unloaded or transferred to receiving points.
Conveyor belt systems have been known and used in many industries for many years. Many of these systems utilize a continuous loop belt to transport bulk materials from one point to another. Traditionally the belt is supported by idler rollers, or troughing rollers which define a conveyor path. The drive means that translate the belt along the conveyor path must be capable of moving the weight of the materials as well as overcoming the frictional forces developed between the belt and the above described support means.
The conveyor systems described above have many drawbacks. First, each of the support rollers is subject to wear and mechanical failure. These failures can damage a belt or cause premature wear of the belt. Second, the rollers require routine maintenance. Often the location of these rollers within the conveyor system will pose significant hazards to maintenance personnel assigned to service these components. Other times, the location of these components will merely be an inconvenience. In either case these difficulties can lead to significant delays or equipment downtime while maintenance personnel service the equipment. Finally, each roller introduces a component of friction into the system, which must be overcome by the belt drive mechanism. These frictional components tend to increase as the rollers and their associated bearings wear, requiring additional energy consumption by the drive mechanism. In turn, the belt drive mechanism is subjected to additional wear, potentially causing premature mechanical failure.
Fluid plenum conveyor belt support elements have been introduced to overcome these limitations. They function by the introduction of a pressurized fluid source between the belt and a trough formed in the plenum to contain and guide the belt. The pressurized fluid forms a fluid film layer between the trough and the conveyor belt. The fluid film supports the weight of the belt and the materials transported thereon, while providing a near frictionless bearing surface between the belt and the trough. This concept provides distinct improvements over earlier roller methods. First, maintenance of the bearings is virtually eliminated by the elimination of the moving components of the earlier roller systems. Second, the fluid film bearing significantly reduces the amount of friction between the belt and supporting conveyor path. Finally, the reduction of frictional forces encountered by the belt permits operation of the conveyor drive mechanism at reduced power levels resulting in reduced energy costs and reduced wear and tear on the belt drive mechanism.
While fluid plenum conveyor systems have many advantages over troughing roller systems, fluid plenum systems in the art demonstrate significant inefficiencies. First, the shape of these fluid plenum troughs inhibits efficient fluid film layer propagation. Second, the fabrication techniques used to form the troughs introduce surface irregularities which become more pronounced in response to operational and environmental factors. These surface irregularities further inhibit efficient propagation of the fluid film layer. Third, the prior art methods used to join discrete trough elements to form a continuous fluid plenum conveyor system introduce further surface irregularities at the joint between each element. Moreover, these junctions do not sealingly join trough elements, permitting the inefficient escape of pressurized fluid from the plenum. Fourth, the fluid plenum troughs of the prior art demonstrate the undesired characteristic of belt float, wherein an unloaded portion of the conveyor belt lifts uncontrollably from the trough. Finally, in applications that transport bulk materials containing or developing significant amounts of particulate matter, the pressurized fluid used to produce the fluid film surface can release the particulate into the environment, creating an environmental hazard.
Prior art versions of fluid plenum conveyors employ a cross-sectional trough shape consisting of a central radius symmetrically extending upward from each side of a vertical centerline. When the central radius reaches a desired angle, the trough is further extended with straight sides extending upward from a point of tangency with the central curve to create a trough of the desired cross section. The intent of the prior art designs was to create a trough with the same cross-sectional profile as prior art troughing rollers in accordance with Conveyor Equipment Manufactures Association, (CEMA) standards. It was thought that a fluid film conveyor trough of the described profile would best permit the intermittent use of standard CEMA troughing rollers in cooperation with fluid plenum troughs to form a continuous conveyor path. While this design more accurately replicates the conventional roller profile, it is not the optimum shape to create a supporting fluid film. Uniform contact of the belt with the trough surface is critical to allow the pressurized fluid to equally react against the entire surface of the belt. The flat tangential sections of the prior art design prevent uniform contact of the belt with trough surface. As a result, fluid flow separation occurring near the boundary of the tangentially flat portions and the curved portion disrupting the propagation of the fluid film layer.
Prior art troughs with tangential sides also exhibit surface irregularities which become more pronounced in response to operational and environmental factors. The surface irregularities primarily manifest themselves along the length of the tangential portions of the trough, and are defined by convex and concave portions interspersed throughout the trough surface. However, the techniques used to join the flat tangential portions to the central radius portion can also distort the surface of the central radius portion. The surface variations cause corresponding variations in the fluid pressure between these portions of the trough and the belt. The concave areas impose a lower pressure against the belt due to the belt bridging across the concave areas. The increased fluid flow across the concave portions further disrupts the propagation of the fluid film layer. Conversely, the convex areas impose higher pressures against the belt. When the pressure between the belt and the convex portions of the trough exceeds the pressure of the fluid film, the belt will come into frictional contact with the trough. In response to operational and environmental stresses, these surface irregularities become more pronounced, further reducing the efficiency of the fluid plenum conveyor system. In an application using air as the supporting fluid, a relatively low operating pressure of 1. PSI is typical. This seemingly low pressure exerts substantial total pressure within the plenum. For example: a trough supporting a 54xe2x80x3 wide conveyor belt has over 15,000. pounds of upward lift on a typical 20. foot long section. When combined with the effects of thermal expansion, these pressures will further distort the surface irregularities in the trough, seriously degrading the efficiency of the system. The resultant effect of all these inefficiencies is an increased power demand from the conveyor drive and blower mechanisms with corresponding wear on the belt, trough, and drive and blower mechanisms.
The prior art methods used to join discrete trough elements to form a continuous fluid plenum conveyor system introduce additional surface irregularities at the joints between each element. Moreover, these joints do not adequately seal joined trough elements, permitting the inefficient escape of pressurized fluid from the plenum. Typically, fluid plenum troughs in the art are joined by a tongue and groove arrangement, wherein a tongue is fixed to the underside of the plenum trough of one member and a groove is fixed to the underside of the plenum trough of a second member. The engagement of the tongue into the groove provides alignment and joining of the trough elements. The tongue and grooves are formed to parallel the contours of the trough elements. By this arrangement, the joint is unable to provide needed support to resist the perpendicular loads imposed on the trough. As a result, it is common to find troughs connected by this technique with an added surface irregularity along the joint. This irregularity will experience further distortion in response to the operational and environmental stresses discussed above. Furthermore, troughs joined by this technique do not include a sealing connection between the trough elements. As a result, considerable energy is lost in a long conveyor system, with even small amounts of fluid leaks at each plenum connection.
The characteristic xe2x80x9cbelt floatxe2x80x9d is another common problem with fluid plenum troughs in the art. The absence of a load to overcome the belt tension, causes the belt to span the center portion of the trough in the same manner as a belt encountering a convex surface irregularity described above. As the belt spans the central radius it lifts uncontrollably from the surface of the trough. In applications employing covers over the conveyor trough, the uncontrolled lifting of the belt can cause damage to the covers and the belt. Moreover, as the belt separates from the surface, fluid flow becomes less restricted, which if left uncorrected, will result in degraded fluid film layer performance over loaded portions of the belt.
The introduction of fluid plenum systems for use in conveyor operations has also created a potential environmental hazard. In operations where significant quantities of particulate products are transported or are created during the transport of bulk products, the pressurized fluid required to develop the fluid film layer tends to entrain the particulate, thereby contaminating the fluid. As a result, control measures are needed to prevent their release to the environment or causing damage to the fluid pressurizing system.
Consequently, there exists a need for an improved fluid plenum trough design that enhances the propagation and maintenance of the induced fluid film surface between the trough and the conveyor belt.
There is also a need to improve the methods of manufacture for the fluid plenum elements to reduce the occurrence of surface irregularities in the trough.
Furthermore, an improved method of joining fluid plenum elements is required to enhance the efficiency of the conveyor system to reduce drive mechanism and fluid pressurizing system loads.
Finally, there is a need to make fluid plenum conveyor systems more environmentally sound.
It is a first object of the present invention to provide a fluid plenum conveyor trough having improved fluid film propagation properties. This is achieved in the present invention by a preferred trough shape comprising a continuous radius extending symmetrically upward from each side of a vertical centerline, the radius created by a curve that would intersect at the midpoint of a standard CEMA roller. The point intersected by the vertical centerline should also be slightly lower than the top edge of the bottom roller of a standard CEMA roller trough. Selection of the radius, as defined above, permits use of a CEMA roller in series with the plenum trough without belt interference at either the receiving or transmitting ends of the plenum trough. By eliminating the flat tangential portions of the prior art trough profile, consistent belt pressure across the trough profile is achieved resulting in more efficient fluid film propagation.
Second and third objects of the invention, directed towards reducing the surface irregularities of the trough and facilitating the manufacturing process, are achieved by selection of the constant radius profile and maintaining the radius throughout the manufacturing process. A continuous radius trough is easily fabricated by either cutting a section pipe having the desired radius or forming a flat material to the desired radius. The continuous radius of the trough section is maintained by use of a precision alignment fixture temporarily securing and aligning a corresponding radius of arcuate end plates during their attachment to opposite ends of the trough section. After attachment of the mating flanges, the plenum is formed around the trough section such that the plenum conforms to the trough. The plenum optionally includes at least one arcuate support gusset enclosed therein, supporting the trough along its length and strengthening the plenum against torsional loads.
A fourth object of the present invention, directed to improve the joining of plenum elements, is achieved by the precision alignment of the arcuate mating flanges, as described above. Since each plenum element is identically formed, joining successive plenum elements in near perfect alignment is easily achieved. Adjoining mating flanges are joined by securing bolts, rivets or other suitable attachment means, received in aligned holes interspersed throughout the periphery of the flanges. To achieve a fluid tight seal, a gasket is compressed between the mating flanges by securement of the attachment means.
A fifth object of the present invention, directed to reducing the deleterious effects of belt float, is achieved by the attachment of tapered wedges to the constant radius portion of the trough. As an unloaded belt portion begins to lift from the trough surface, the edges of the belt encounter the tapered wedges. The wedges controllably lift the belt from the trough surface, facilitating purging of excess fluid from beneath the belt. The purging of excess pressurized fluid reduces the lifting energy imparted to the belt thereby preventing uncontrolled floating of the belt.
A final object of the present invention is directed towards controlling particulate release into the environment or contamination of the fluid pressurization system. This is achieved by the use of a fluid knife to clean particulate matter from the belt shortly after it has deposited the transported product to the delivery point. The fluid knife impinges the surface of the belt to dislodge the particulate matter and entrain it with the fluid and a larger mass fluid volume flow. The entrained particulate is then ducted to a standard filtration system, such as a bag house as such devices are commonly known by in the art.